1. Field of the Invention
The present invention generally relates to systems for modeling the behavior of integrated circuits such as verifiers, simulators and design tools, and more particularly to a computer program that includes modeling of digital integrated circuit power distribution network current waveforms.
2. Description of Related Art
Design tools and verification tools are necessary for modeling large-scale digital integrated circuits such as Very Large Scale Integration (VLSI) circuits. Millions of transistors and logic gates are often combined on a single die and the performance of the die is modeled using software that models the performance of the overall die based on known (modeled) performance of individual gates, inverter/buffer models of gates, or models of larger functional blocks.
Power supply current for individual gates or blocks combines to generate the power requirements for the overall die, and will typically combine in sub-groups to several power and ground pins that are connected external to the integrated circuit package. The power supply pin connections are typically inductive, while the external power supplies to which the power pins connect are typically capacitive loads. The inductive pin characteristic leads to voltage noise as the changing power supply currents generate voltage drops across the pin inductances. Therefore, knowledge of power supply currents at power nodes of logic gates or larger functional blocks is valuable for knowing overall current consumption and time-dependent behavior and for induced/radiated noise modeling. The overall current consumption along with the power supply voltage(s) determine power dissipation, which must also be determined for analysis of thermal characteristics and failure rates of an integrated circuit.
A large component of the power supply current generated in Complementary Metal Oxide Semiconductor (CMOS) integrated circuits is the short-circuit, or “cross-conduction” current drawn by the transistors of a complementary pair at times when the complementary pair switches state and both transistors conducting. Short-circuit current modeling is critical for accurate modeling of the power distribution network analysis. The short-circuit current can also be largely determinative of power dissipation within a CMOS integrated circuit, which is often referred to as short-circuit power. Therefore, it is critical also to accurately model short-circuit current in order to model device power dissipation.
Present techniques for short-circuit current and short-circuit power modeling typically calculate the short-circuit currents based on formulas derived for specific circuits using simplified device models, such as an inverter model with a capacitive load. Another technique is a table-based approach that requires extensive circuit simulation and memory resources to determine exact circuit performance separate from the timing simulations. The present short-circuit modeling techniques used typically are not integrated with timing models for the logic circuits and thus the short-circuit and timing performance modeled may not be consistent. Further, the simplified models presently used for short-circuit current modeling are not integrated with more sophisticated analytical models used within the timing analysis and for those reasons produce results with a low accuracy and cannot accurately determine the short-circuit current for complex circuit models such as logic circuits having reactive loading parameters.
Therefore, it is desirable to implement an improved CMOS short-circuit current and short-circuit power modeling algorithm. It would further be desirable to provide an algorithm that is compatible with existing circuit timing models.